Development of Anode Materials for Solid Oxide Fuel Cells A Review

摘要

Solid oxide fuel cells (SOFCs) are electrochemical devices that provide significant advantages over the conventional power generation resources. Despite all these firm advantages there still remain a number of hurdles that have to be crossed before moving on for the viable commercialization of the solid oxide fuel cells (SOFCs). Most important of these hurdles primarily include the working temperature zone, proper materials selection for the electrodes, electrolytes, interconnects and the compatibility of the components! In this review, primarily the materials properties of the anodes are being evaluated and the mixed ionic electronic conductors (MIECs) being explored as the most probable candidates. Different constraints on the MIECs are outlined, and the possible paths to an improved anode are portrayed. The present situation is forcing the SOFC community to explore electronically conductive composites capable of conducting ionic species (MIECs) also at the anode. Most MIEC perovskites facilitate oxide-ion conduction via oxygen vacancies, whereas La{sub}(1-x)Sr{sub}xTiO{sub}(3+δ) have a few mobile oxygen vacancies in the perovskite matrix. The ionic conductivity of Sr{sub}2Mg{sub}(1-x)Mn{sub}xMoO{sub}(6-δ) is ～10 S/cm at 8000℃ in H{sub}2 and the system gives sulfur tolerance and excellent anode performance. La{sub}0.8Sr{sub}0.2Ga{sub}0.83Mg{sub}0.17O{sub}2.815 (LSGM) was used as electrolyte and SrCo{sub}0.8Fe{sub}0.2O{sub}(3-δ) as cathode in a system and the maximum power density(P{sub}(max)) achieved was 0.84 Wcm{sup}(-2) at 8000℃ and 0.45 Wcm{sup}(-2) at 7000℃ resp. in H{sub}2. The addition of Rh as a noble metal to a Cu/SDC anode improved the cell performance significantly in methane. Ce{sub}0.84Ti{sub}0.15Pt{sub}0.01O{sub}(2-δ) has shown good reducibility compared to Ceria and high catalytic activity for partial oxidation towards hydrocarbons. This material is yet to be tested in SOFC environment with Platinum metal. Introduction of cobalt was claimed to improve the thermal stability of the Cu-based cermets in CO fuels compared to H{sub}2 at 8000℃, producing the power densities of 310 mW cm{sup}(-2) in H{sub}2 and 370 mW cm{sup}(-2) in CO. Mixed-conductors are the subject of most active researches and the prominent materials so far investigated are Zr/Ti/Y/O, La/Cr/O, La/Sr/Co/Fe/O, La/Sr/Cr/V/O, La/F e/Y/Sr/Ti/O, La/Sr/Cr/NiO etc. These compositions were studied as novel anodes but somehow produced less catalytic activity compared to that of Ni composites. With (LSGM) as electrolyte, SrCo{sub}0.8Fe{sub}0.2O{sub}(3-δ) as the cathode and LDC as buffer layer, a porous composite anode of Ni and La-doped ceria exhibited a power density as high as 1.4Wcm{sup}(-2) at 8000℃ in H{sub}2 and seems to be highest so far published in literature at that temperature. In another case, H2S is oxidized by the mixed-valent La{sub}(1-x)Sr{sub}xVO{sub}(3-δ) (LSV) perovskite, which makes an SOFC with LSV- anode tolerant to 10% H{sub}2S in H{sub}2, but the P{sub}(max) generated was far from being competitive. Since Doped Cerias are proved to be tolerant to sulfur poisoning and found to replenish O{sub}2-ions to the reactive surfaces in order to prevent coke buildup; the next prudent and logical step is to explore other oxides that are MIECs in the reducing atmospheres at the anode and are catalytically more active than ceria for hydrocarbons. At this moment, there are a number of potential alternatives to the Ni or Cu-based anodes in the field of 'novel-anode' search. The catalytic activity of most of the promising oxides needs to be elevated with the infiltration/impregnation techniques done at low enough temperatures. The prime intention of this article is to highlight the contribution that materials engineers have made to the efficient development of Anodes of the SOFCs.